This journal is c the Owner Societies 2012 Phys. Chem. Chem. Phys., 2012, 14, 9311–9316 9311 Cite this: Phys. Chem. Chem. Phys., 2012, 14, 9311–9316 The electronic structure of Ge 9 [Si(SiMe 3 ) 3 ] 3  : a superantiatom complexwz P. Andre Clayborne* a and Hannu Ha¨kkinen* ab Received 13th October 2011, Accepted 26th January 2012 DOI: 10.1039/c2cp23229d We report on the electronic structure of Ge 9 [Si(SiMe 3 ) 3 ] 3  . Systematic density functional theory analysis of the electronic shell structure of the cluster and its derivatives reveals that the Ge 9 [Si(SiMe 3 ) 3 ] 3  and its neutral counterpart have electronic shells that can be explained using the superatom model. The ligand–core interaction of these complexes is distinctly different from previously identified gold, gallium, and aluminium superatom complexes, indicating an electron- donating rather than electron-withdrawing ligand. We modify the electron-counting rule for this case and introduce a simple picture for superatom and superantiatom complexes. Discussions comparing shell models, Zintl clusters, the superhalogen Al 13 and superatom complexes to Ge 9 [Si(SiMe 3 ) 3 ] 3  are presented. Introduction Zintl anions, known since the work of Joannis in the 1890s, are post-transition metal clusters with the ability to exist in multiple charged states. 1,2 These clusters isolated in Zintl phases are crystallized with countercations through various experimental techniques. 3 Typically E 9 x Zintl clusters (E = Si, Ge, Sn, and Pb; x = 2–4) are nine-atom cages whose geometry has been explained primarily using the Wade–Mingos rules to account for the number of vertices on the subsequent cages. Wade–Mingos rules correlate the shape of the cluster with the number of skeletal electrons as first used for boranes and carboranes. 4 The concept of applying these rules to post-transition metal clusters was realized by Corbett in the 1960’s and has since been applied to a series of nine-atom Zintl clusters. 5 The study of Zintl clusters has grown to include the so-called ‘‘functionalization’’ of germanium clusters. 6–8 Functionalization requires the addition of an organic substituent to the Ge 9 4 cage. For example, the nine-atom germanium cluster ligated by two diphenylbismuth groups was successfully synthesized by Ugrinov and Sevov in 2001. 6 Sevov and co-workers have illustrated through the alkenylation of Ge 9 resulting in a variety of organo-Zintl compounds. 7 Further, there has been documented success of the Ge 9 4 Zintl cluster interacting with transition- metal and noble metal compounds. 8 Recently, the study of nine-atom germanium clusters and their interaction with ligands has been extended to include metalloid clusters. 9 Metalloid clusters have metal–metal bonds which outnumber the metal–ligand bonds. 10 Thereby the cluster has both ‘‘naked’’ and ligand-bound atoms. Synthesized by Schnepf, the Ge 9 {Si[SiMe 3 ] 3 } 3  cluster (Fig. 1A) and its neutral counterpart have been studied for their uses as molecular cables and building blocks for supramolecular chemistry. 9,11 In the case of the Zintl polyanion, Ge 9 4 , its stability has primarily been explained within the construct of Wade–Mingos Fig. 1 Relaxed geometries of (A) Ge 9 [Si(SiMe 3 ) 3 ] 3  (1), (B) Ge 9 [SiH 3 ] 3  (3) and (C) Ge 9 H 3  (2). The gold, purple, grey and white balls represent the germanium, silicon, carbon and hydrogen atoms, respectively. a Department of Chemistry, Nanoscience Center, FI-40014 University of Jyva ¨skyla ¨, P.O. Box 35, Jyva ¨skyla ¨, Finland. E-mail: penee.a.clayborne@jyu.fi; Fax: +358 14 260 4756 b Department of Physics, Nanoscience Center, FI-40014 University of Jyva ¨skyla ¨, P.O. Box 35, Jyva ¨skyla ¨, Finland. E-mail: hannu.j.hakkinen@jyu.fi; Tel: +358 40 024 7973 w This contribution is dedicated to Professor Ludger Wo¨ste for his 65th birthday. z Electronic supplementary information (ESI) available: The structure of 1, 2, and 3 with a table of the bond lengths and dihedral angles and projected density of states for the Ge 9 Na 3  cluster. The table of the HOMO–LUMO gaps for superatoms and superatom complexes. The angular-momentum-projected electron density of states for Ge 9 and Ge 9 [Si(SiMe 3 ) 3 ] 1  . See DOI: 10.1039/c2cp23229d PCCP Dynamic Article Links www.rsc.org/pccp PAPER Published on 27 January 2012. Downloaded by Jyvaskylan Yliopisto on 20/02/2015 09:51:05. View Article Online / Journal Homepage / Table of Contents for this issue